A Turkish prosecutor has demanded that arrest warrants be issued against two Saudi nationals close to Crown Prince Mohammed bin Salman over the murder of journalist Jamal Khashoggi, a Turkish source close to the investigation said Wednesday.

Khashoggi, 59, was killed shortly after entering the Saudi consulate in Istanbul on October 2 to obtain paperwork for his upcoming marriage.

The chief prosecutor's office in Istanbul filed an application Tuesday to obtain the warrants for Ahmad al-Assiri and Saud al-Qahtani, described in court documents as being "among the planners" of the murder of the Washington Post contributor Khashoggi.

Assiri often sat in during Prince Mohammed's closed-door meetings with visiting foreign dignitaries and Qahtani was a key counsellor to the crown prince. Both were sacked after Riyadh admitted Khashoggi was killed in the Saudi consulate.

According to Turkey, a 15-member Saudi team was sent to Istanbul to kill Khashoggi.

Turkish President Recep Tayyip Erdogan has said the order to kill Khashoggi came from the highest levels of the Saudi government, but has insisted it was not King Salman.

Riyadh has since detained 21 people over the murder. Despite speculation that the powerful crown prince ordered the hit, the kingdom has strongly denied he was involved.

But two key US Republican senators said a Tuesday briefing by the CIA's director only strengthened their conviction that Prince Mohammed directed the murder.

The Istanbul prosecutor in charge of the investigation said in late October that the Saudi former insider turned critic was strangled then his body was cut into pieces.

The remains of Khashoggi's body have not been found.

There has been speculation in pro-government media that his body was dissolved in acid.

A senior Turkish official Wednesday said the prosecutor's move "reflects the view that the Saudi authorities won't take formal action against those individuals".

The official, who did not wish to be named, pointed to the fact that the wording of the prosecutor's request suggested that the current list wasn't necessarily exhaustive, appearing to indicate that more arrest warrants could be sought.

Amid criticism from Ankara over Saudi Arabia's lack of cooperation with the Turkish investigation, the official said Riyadh could "address those concerns" over its commitment to probing the murder by extraditing all the suspects to Turkey.

What a hypocrite! The Assad regime crimes are worse hundred fold than that of the Saudi regime and you support it. The Iranian regime executed far more dissidents than the Saudi regime and yet you support it.

What a hypocrite! The Assad regime crimes are worse hundred fold than that of the Saudi regime and you support it. The Iranian regime executed far more dissidents than the Saudi regime and yet you support it.